Brain Size in Autism: Some New Preliminary Reports

I attended a conference last week in La Ciotat, France, called the EMBO Conference on Brain Development and Disorders. While the title may suggest a width breadth of research, it has come to primarily focus on autism, although focuses on syndromic forms as well. The conference has been organized and hosted by Dr. Yehezkel Ben-Ari for a number of years now and gives researchers the opportunity to get a more in-depth look at other researcher’s work, to network, and– of course– to enjoy the gorgeous French coastline. Ben-Ari is clearly very proud of his home city and with good reason: it is a slice of Mediterranean heaven.

I also had the opportunity to talk with and get to know David Amaral a little better. He works at the UC Davis M.I.N.D. Institute in California, heading up the research division. Incidentally, I also learned that he’s an avid lover of seafood. I gave the mini-octopus the old college try as per his recommendation but I think I’ll leave that delicacy to him at future meetings. On the other hand, the chorizo cream-covered scallops were DELICIOUS. 😉

Anyways, I digress. David gave his talk the final day of the conference and the purpose of my post here is to impart some of his team’s preliminary findings on a longitudinal MRI study of autism which I think readers will find very interesting. I’d like to stress, however, that many of these are preliminary only, so definitely keep an eye out for future publications from his team.

The title of his presentation was, “Neuroimaging the Full Spectrum of Autism”, and they’ve done precisely that. Sadly, most researchers have veered away from studying moderate- and low-functioning autistic individuals when it comes to MRI studies because it can be such a challenge to get them to cooperate and remain still for the necessary period of time. If any of you have ever had an MRI performed, say for an injury or chronic illness, you’ll probably remember how long you had to remain motionless just so the machine could acquire the images.

David’s team has done some phenomenal work, working with the kids to train them, along with much help from the parents, to actually fall asleep inside the scanners and thereby remain still for the duration of the scan. I won’t go into specifics, but it involves a good deal of desensitization and practice. But in the end, they’ve had phenomenal success rates (80-90%+). So they’ve been able to follow autistic kids via MRI from age 3 onwards, taking scans each subsequent year.

One thing David says they’re finding so far is that average brain volume is larger in autism– a finding most would probably already be familiar with. However, this is actually a reflection of about 15% of that population which has megalencephaly (abnormally large brains), a trait that starts to emerge around 4-6 months of age. At the other extreme, another minority of that population also has microcephaly. However, the majority of the autistic kids’ brain volumes fall within the control ranges. Most interestingly, about 88% of those kids with bigger brains also exhibit autistic regression and tend to be more severely affected.

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Image showing larger brain volume in the regressive form of autism. Image borrowed from here.

Longitudinally, it’s starting to look like Redcay and Courchesne’s original report about brain volume leveling off in adolescence in autism is inaccurate. Currently, at age 9, those kids with megalencephaly have shown a steady trajectory of brain growth and do not appear to be leveling off towards “normal”. Instead, David suggests that because there have been trends to image only high-functioning individuals in adolescence, more severely-affected megalencephalic individuals have probably been underrepresented.

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David also reported that, as has been suggested previously, the average body size for age is somewhat larger in autistic children. Although, interestingly, those kids who are taller for their age are not the same ones with the larger brains; thus they’re two separate subgroups and megalencephaly can’t be accounted for by larger bodies in this sample.

I’m really looking forward to further data that comes from this longitudinal study at the M.I.N.D. Institute; for instance, whether their predictions of brain volume trajectory into adolescence and adulthood hold true. I also truly applaud this team for being bull-headed enough to do what most people thought impossible: namely, scanning the full spectrum of autism.

2 responses to “Brain Size in Autism: Some New Preliminary Reports

  1. Sometimes researchers use exclusionary criteria to exaggerate their findings and interpretations. Simon Baron-Cohen has done this in his amniocentesis testosterone studies. His well referenced paper that reported testosterone prenatal levels in newborns excluded cases of genetic syndromes, significant pre peri and neonatal problems even fetal alcohol syndrome. Klinefelter syndrome and fetal alcohol syndrome, excluded from his studies, both have been found to have low levels of postnatal testosterone.

  2. Ah, very interesting, Robert. Somehow that doesn’t shock me about Baron-Cohen. Very nice guy, but he strikes me more as a “generalizer” or a “lumper” rather than a splitter.

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